Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $62.96   3.468%   $65.1435   $65.14   $65.15   $65.10  
  Purchase #2 $235.81   11.541%   $263.0248   $263.02   $263.00   $263.00  
  Purchase #3 $197.94   4.478%   $206.8038   $206.80   $206.80   $206.80  
  Purchase #4 $70.53   6.334%   $74.9974   $75.00   $75.00   $75.00  
  Purchase #5 $27.90   9.302%   $30.4953   $30.50   $30.50   $30.50  
  Purchase #6 $72.47   8.552%   $78.6676   $78.67   $78.65   $78.70  
  Purchase #7 $185.79   6.432%   $197.74   $197.74   $197.75   $197.70  
  7 purchase totals = $853.40       $916.8724   $916.87   $916.85   $916.80